Inactivation, by light

Properties Pteroylglutamic acid Orange-yellow needles or platelets tasteless odorless. Slightly soluble in methanol and sparingly soluble in water insoluble in acetone, ether, benzene moderately soluble in dilute alkali hydroxide and carbonate solutions stable in heat in neutral and alkaline solution destroyed by heating with acid inactivated by light. 

Finally, it should be noted that coenzyme B g would probably have been discovered by Beck et during their studies of the conversion of methylmalonyl-CoA to succinyl-CoA by the sheep kidney mutase (isomerase) were it not for the fact that this enzyme binds the coenzyme very tightly in such a way that it is not susceptible to inactivation by light. Because of these properties they were unable to obtain a coenzyme-free mutase and so concluded that the reaction probably has no cofactor requirement. 

The dry crystals are stable for months in the dark, but aqueous solns decompose on exposure to VIS or UV light or alkaline CN", but stable in the dark at pH 6-7. The vitamin is inactivated by strong acids or alkalies. [Barker et al. J Biol Chem 235 480 1960 see also Vitamin B/2 (Zagalak and Friedrich Eds) W de Gruyter, Berlin 1979.]... 

Mnemiopsin is inactivated by the exposure to light over its entire absorption spectral range, and the inactivation cannot be reversed by keeping the inactivated material in the dark, which differs from the specimens of a live animal. The photoinactivation is accompanied by a partial loss of the 435 nm absorption band, which is probably due to the decomposition of the peroxidized coelenterazine in the protein. 

Heat is the most reliable method of virus disinfection. Most human pathogenic viruses are inactivated following exposure at 60°C for 30 minutes. The virus of serum hepatitis can, however, survive this temperature for up to 4 hours. Viruses are stable at low temperatures and are routinely stored at -40 to -70°C. Some viruses are rapidly inactivated by drying, others survive well in a desiccated state. Ultraviolet light inactivates viruses by damaging their nucleic acid and has been used to prepare viral vaccines. These facts must be taken into account in the storage and preparation of viral vaccines (Chapter 15). 

Recendy, PEN, a-4-pyridyl-oxide-N-t-butyl nitrone (POEN) or 5-5,dimethyl-1, pyrroline-N-oxide (DMPO) were evaluated in models of experimental shock (endo-toxic, traumatic and mesenteric artery occlusion in rats). All three nitrones, when given prior to the insult intraperitoneally, were protective. When the nitrone s spin trapping ability was inactivated by exposure to solar light and air, they were no longer efficacious (Novelli, 1992). 

Figure 9.4 Repair of DNA inactivated by ultraviolet light. Light causes die dimerization of adjacent thymine residues that block DNA replication. The four enzymes shown are involved in removal and replacement of a portion of the DNA that contains the dimer.

Anderson, L. E., T.-C. L. Ng, and K-E. Y. Park. Inactivation of pea leaf diloro plastic and cytoplasmic glucose 6-phosphate dehydrogenases by light and dithio-threitol. Plant Physiol. 53 835-839, 1974. 

The presence of proflavine protects some viruses against inactivation by ultraviolet radiation and proflavine has been shown to inhibit formation of thymine dimers in DNA.86 (6) The sensitivity of microorganisms to ultraviolet light increases with, but is not proportional to the square of, the thymine content of the DNA.86 (7) Substitution of... 

Oj had fallen considerably in particles prepared from the anaerobically stimulated cells. Whether a third type of inactivation was the explanation for these observations is not clear. Certainly the very low of the oxidase of Oj of 10 pM might indicate that only the most rigid measures would exclude Oj sufficiently to abolish the enzymic turnover in PMNs. Therefore, the partial effect of anaerobiosis might have been to slow both enzymic turnover and the consequent autoinactivation found by Light et al. in the partially purified enzyme. 

Frankel and Tarassuk (1959) exposed a layer of raw skim milk 1 cm thick to direct sunlight at room temperature and noted a loss in lipase activity of 84% in 5 min and of 96% after 10 min. In diffuse daylight inactivation was reduced but 71% of lipase activity was lost in 1 hr. The loss of activity by light was independent of the temperature of the milk, equal losses being observed at 0°C and at 37°C. The enzymes were markedly protected against light inactivation by the presence of fat. 

From an analytical perspective, the single most important physicochemical characteristic of riboflavin is its photosensitivity (80-82). Exposure of this vitamin to ultraviolet and visible light results in irreversible photoreduction to lumiflavin and lumichrome and loss of vitamin activity. In addition, the coenzymes are subject to hydrolysis by endogenous phosphatases that are present in a number of foods. Since these enzymes are generally inactivated by thermal processing, they are a concern only in the analysis of fresh products. 

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